The lift, which can carry 40 passengers, takes visitors from the ticket office at road level to the high level walkways which are 140 feet above the river.

A report published this week for members of the City of London Corporation's City Lands & Bridge House Estates Committee confirms that the Health & Safety Executive's investigation into the lift failure is still ongoing.

"In recent communications, the HSE has indicated that this is a complex investigation involving up to four duty holders (including the City of London)," says the report from the Town Clerk.

"Substantial focus in the investigation appears to be directed towards the design of the counterweight and roping systems of the lift. "

The document sets out the action taken by the City of London Corporation in the wake of the incident, including inspections of other passenger-carrying lifts in buildings owned by the authority, such as those at the Barbican Centre.

The report concludes: "The malfunction at Tower Bridge was attributed to a failure of the counterweight mechanism. Why this happened is the focus of the ongoing HSE investigation which is still in progress.

"The City of London secured external expertise to design and carry out this refurbishment project. As already pointed out, the HSE investigation is wide ranging and other aspects may arise."